All spell casters gain their abilities through a form of demon possession. So in order to gain magical abilites, PCs must track down and trap demons. Of course there are some pretty powerful demons, if the demon is stronger than the PC, the PC could find themselves subjugated to the Demon's will.
The ancient Empire of the Golden Crystal fell so long ago that little is known of them besides their legendary magical power. Supposedly, in the Golden Age of the Crystal Empire, cities were filled with enchantment, spells far beyong the ability of modern magi.
A tomb robber has returned to civilization with something never seen before: Ceramic vials of reddish dust that supposedly enhance a magician's power tremendously when the dust is sprinkled upon the floor of his workroom. The rogue selling the vials claims that they were recovered from a ruin of the Crystal Empire, but can he be believed?